1. Field of the Invention
The present invention relates to a full-circumferential flow pump and, more particularly, to a full-circumferential flow pump which has a motor, an outer cylindrical pump casing enclosing the motor, and an annular space formed between a motor frame barrel provided around a stator of the motor and the outer cylindrical pump casing.
2. Description of the Related Art
It has been customary to press sheet steel such as stainless steel to form a pump casing according to a deep drawing process, and then weld or otherwise fasten a suction or discharge flange to the pressed pump casing. The pump casing thus fabricated is liable to be deformed due to the internal pressure developed in the pump casing itself and also external forces applied to the pump casing from piping connected thereto. Any deformation that the pump casing suffers should be reduced to such a level that the pump casing will never be in contact with an impeller housed in the pump casing. Therefore, the pressed pump casing must meet mechanical strength requirements for bearing loads including external forces applied from the connected piping and internal pressure developed in the pump casing, and also rigidity requirements for maintaining a desired clearance between a liner ring and the impeller.
Inasmuch as the pressed pump casing is of a relatively flexible structure with respect to applied loads, it is impossible for the pressed pump casing itself to satisfy both the mechanical strength requirements and the rigidity requirements. To achieve a desired level of rigidity, conventional pressed pump casings have employed a steel sheet having a thickness greater than the thickness required to withstand an internal pressure developed therein, or a reinforcing member of complex shape attached thereto.
As described above, conventionally, in order to prevent the pump casing or the liner portion thereof from being deformed, the rigidity of the pump casing has been increased by employing either a steel sheet having a thickness greater than the thickness required to withstand an internal pressure developed in the pump casing or a reinforcing member of complex shape attached thereto. The steel sheet of increased thickness is, however, difficult to press to shape, and the reinforcing member of complex shape results in an increase in the cost of manufacture of the pump casing.